1. Field of the Invention
The present invention relates to an indexable drill and a drill body of the indexable drill.
2. Description of the Related Art
Japanese Patent Laid-Open No. H06-91416(1994) discloses an indexable drill with a plurality of rows of grooves formed in a wall surface of a chip discharging groove and extending along an axis direction of a drill body. Chips contact only the plurality of surfaces formed by the plurality of rows of grooves. This reduces the contact area between the wall surface and the chips and thus a possible frictional force exerted between the wall surface and the chips. This enables the chips to be effectively urged to be discharged. Thus, the chips can be smoothly removed when a bore with a relatively large L/D is processed or when a difficult-to-machine material such as stainless steel or soft steel is bored; the L/D is the ratio of the depth L to diameter D of a bore.
In the indexable drill disclosed in the above publication, the plurality of rows of grooves formed in the wall surface of the chip discharging groove enable a reduction in the contact area between the wall surface of the chip discharging groove and the chips. On the other hand, the amount of friction between the plurality of rows of grooves and the chips may increase, thus making the surfaces of the plurality of rows of grooves easily worn away. Thus, disadvantageously, the effect of urging the chips to be smoothly discharged fails to last long. Furthermore, the above-described indexable drill uses a central edge insert and an outer peripheral edge insert for boring. Attachment seats for the respective two inserts provided at a leading end portion of the drill body form thinned wall portions that are thinner than the other portions. Hence, disadvantageously, when a strong force is applied to the thinned wall portions during boring, the thinned wall portions are easily broken.